1870.] 



Mineral Constituents of Meteorites. 



153 



showing them to be enstatite under different aspects. "When lime is ab- 

 sent it presents itself as a simply prismatic mineral, the dark-grey tabular 

 variety. When lime is present, though to an amount less than two per 

 cent., the crystalline structure becomes more complex. The augite may 

 perhaps be tessellated, as it were, in the enstatite, somewhat as this latter 

 mineral has been shown to occur intercalated to a small amount in layers 

 of augite. I did not succeed in establishing this point, however, by an 

 examination of microscopic sections of this mineral. 



The crystalline fragments frequently show, when examined by polarized 

 light, a composite structure, the principal sections of the different parts of 

 the mineral being disposed at every angle of mutual inclination. 



The analysis of these minerals yielded the following numbers : — 



Dark Grey Tabular Variety. 



Transparent White Variety. 



Silicic acid. 

 Magnesia . . 



Lime 



Iron oxide. 

 Potash 

 Soda 



Per- 

 centages. 



Oxygen 

 ratios. 



r 



Per- 

 centages. 



Oxygen 

 ratios. 



57*597 



30-718 



58-437 



31-166 



40-64 



16-238 



38-942 

 1*677 



15-564 

 0-479 



1438 





1-177 





0-394 





0-332 





0-906 





0-357 





100-975 





100-922 





Semitransparent Grey Variety. 



, A — ■ , 



Per- Oxygen Per- Oxygen Per- Oxygen 



centages. ratios. centages. ratios. centages. ratios. 



L ii. m. 



Silicic acid.. 57-037 30-419 57'961 30'912 57*754 30*802 



Magnesia ... 40-574 16-117 39*026 15*598 38-397 15*247 



Lime 2-294 0 655 1*524 0*435 2-376 0-678 



Iron oxide.. 0-867 0-154 0*423 



Potash 0-569 0*569 



Soda 0*68 0*657 



Lithia 0*016 



100-772 99-914 100*192 



As in the case of the augite, the soda is probably derived from the hy- 

 drogen chloride ; the iron occurs partly as metal, minutely subdivided, 

 partly as oxide combined with the magnesium silicate. In each case the 

 bases slightly exceed the amount required by the formula of enstatite. On 

 comparing these with known analyses, aud those which I shall shortly sub- 

 mit to the Society, it seems highly probable that, where the conditions 

 under which a meteoric silicate has been formed were such that silicic acid 

 was present in excess of that required by the formula of enstatite, this acid 



